Current demineralization or softening systems often make use of ion exchange resins, e.g. in water purification plants, or softening chemicals, e.g. in laundry washing-machines and dishwashing-machines. The main disadvantage of the resins is that they loose their ion exchange capacity after a period of time and need to be regenerated. This regeneration step involves the use of additional chemicals like acids, bases or salts. These chemicals are harmful for the environment because they can cause salinisation. The same holds for softening chemicals used in washing formulations used in laundry washing-machines and dish washing-machines. Salinisation is known as the accumulation of soluble mineral salts near the surface of soil, usually caused by the capillary flow of water from saline ground water. Where the rate of surface evaporation is high, irrigation can exacerbate the problem by moistening the soil and causing water to be drawn from deeper levels as water evaporates from the surface. The evaporation of pure water leaves the salts behind, allowing them to accumulate, and they can reach concentrations that are toxic to plants, thus sterilising the land.
Alternative demineralisation or softening systems can be based on thermo-regenerable ion exchange resins. These resins can be regenerated at lower or higher temperatures than the temperature at which they are used without the addition of chemicals. Various systems and resins are discussed in WO 2009/028944, incorporated by reference.
WO 2009/028944 discloses a process for separating a charged species from an aqueous system, said process comprising the steps of: (1) contacting a first aqueous system comprising the charged species at a first temperature with an ampholytic polymeric system comprising cationic and anionic domains, wherein the charged species is bonded to the ampholytic polymeric system, and (2) contacting the ampholytic polymeric system with a second aqueous system at a second temperature, wherein the charged species is released to the second aqueous system, wherein the second temperature is higher than the first temperature and wherein the second temperature is less than 60° C. The ampholytic polymer system is preferably a (semi)-IPN having anionic and cationic domains and is prepared by copolymerising at least a LCST-monomer, a cationic monomer selected from the group consisting of vinyl and isopropenyl monomers containing a cationic form of alkyl or aryl amines or of nitrogen-containing heterocyclic aromatic compounds, and a anionic monomer selected from the group consisting of vinyl and isopropenyl monomers containing an anionic group, e.g. an acid such as carboxylate, sulfonate, phosphate, phosphonate, phosphinate, preferably a carboxylate. Example 1 discloses the synthesis of a semi-IPN from NIPAAm (N-isopropyl acryl amide), PANa (sodium polyacrylate), DMBzEA3mCl (acryloyloxyethyl-(benzyl) dimethylammonium chloride), NPAM (N-piperidyl acryl amide), the cross-linker MBAAm (N,N′-methylenebisacryl amide), and the catalyst system APS (ammonium persulfate)/TMEDA (N,N,N′,N′-tetramethyl-ethylenediamine). The charged species to be separated may be cationic or anionic, preferably metal cations and anions derived from organic acids, respectively.
However, the ampholytic polymeric system according to WO 2009/028944 has certain drawbacks, in particular insufficient mechanical properties caused by high swelling ratios and in particular an insufficient desorption performance for Cu2+-ions. Moreover, the ampholytic polymeric system according to WO 2009/028944 can only be used over a limited pH-range, i.e. >4.5. Furthermore, the synthesis methods for ampholytic polymer systems described in WO 2009/028944 lead to irregular shaped granules, which cause unwanted flow anomalies in most process designs.
C. K. Trinj et al., Angew. Makromol. Chem., 212, 167-179, 1993, discloses complexes of polyanions and polycations. These complexes can be split into two oppositely charged polyelectrolytes above a certain critical ionic strength. It is shown that in general complexes consisting of polyanions with strongly acidic sulfonate groups and polycations with strongly basic quaternary ammonium groups have a critical ionic strength that is much higher as compared to complexes consisting of polyanions with weakly acidic carboxylate groups and polycations with strongly basic quaternary ammonium groups, which indicates that the latter complexes have generally a weaker ion pair formation.
N. Gundogan et al., Macromol. Chem. Phys 205, 814-823, 2004, discloses the synthesis of hydrogels by APS/TMEDA catalysed free-radical polymerization of N,N-dimethyl acryl amide and bis(acryl amide) in aqueous solution at various monomer concentration and at a fixed crosslink density. The monomer concentration was varied between 0.37 mol/l and 9.7 mol/l.
C-F. Lee et al., J. Polym. Sci., Part A, Polym. Chem. 41, 2053-2063, 2003, discloses polymer particles prepared by emulsion polymerization of NIPAAm and chitosan. Chitosan is a linear polysaccharide composed of randomly distributed β-(1-4)-linked D-glucosamine (deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit).
H. Macková et al., J. Polym. Sci., Part A, Polym. Chem. 45, 5884-5898, 2007, discloses magnetic microspheres prepared by emulsion polymerization of NIPAAm and MBAAm in the presence of γ-Fe2O3 nanoparticles.
H. Tokuyama et al., Reactive & functional polymers, 67, 136-143, 2007 and H. Tokuyama et al., Reactive & functional polymers, 70, 610-615, 2010, and K. Mizoguchi et al., Separation and purification technology 75, 69-75 2010 disclose different thermoresponsive polymeric systems that are capable of adsorbing heavy metal ions, like Cu2+, Pd2+ and Au3+, at higher temperature (40°-60° C.) and desorption at room temperature. These systems have a desorption temperature which is lower as compared to the adsorption temperature, which is disadvantageous for a lot of processes, because in general ions need to be removed more often from sources of natural water which are most at ambient temperature levels. Furthermore, the systems suffer from a high adsorption degree even at the desorption temperature, which is not beneficial for cyclic processes, especially when low ion concentrations need to be removed.
US 2007/0043189 relates to an amphoteric copolymer of the structure (A), wherein R1 is H or CH3; R2 is a hydrogen atom, or an alkyl group, a cyclic aliphatic group or an aryl group, having 1 to 10 carbon atoms; D is H or COOR3, R3 is a hydrogen atom, or an alkyl group, a cyclic aliphatic group or an aryl group, having 1 to 10 carbon atoms, or a cationic salt group; Z is an O atom or an NH group; A is a —COO group, a —SO3 group or an acid form; a, b, and c is an integer from 1 to 5000; and p and q are integers from 1 to 10. An example of an amphoteric copolymer (A) is copolymer PAMD (B), wherein PAMD is defined as a linear terpolymer of 2-acrylamido-2-methylpropane sulfonic acid (AMPSA), methacrylic acid (MMA) and (α-N,N-dimethyl-N-acryloyloyethyl)ammonium ethanate (DAAE).

Amphoteric copolymer (A) is prepared by a reaction wherein the three monomers are polymerized to form said terpolymer. For example copolymer PAMD (B) is prepared by reacting monomer DAAE with the monomers AMPSA and MAA through a free radical polymerization. The amphoteric copolymers (A) according to US 2007/0043189 are used to improve the fluidity and fluidity retention of cementitious materials.